I was thinking to use some wood pieces to secure the tank to the top of the pillars. That way it's not cemented on, and is still secure. I think a stiff wind could move the tank if it were empty, and I'd like for it not to get blown over.

I'll definitely be putting a mesh screen over the inlet, as mosquitos are a big problem here. It'll also serve the purpose of keeping out leaves. We have a lot of trees on property, and I'd like for my water tank to not be full of leaves.